Aluminum base alloys



Patented Sept. 18, 1951 ALUMINUM BASE ALLOYS Charles B. Willmore, NorthAurora, 111., assignor to William F. Jobbins, Incorporated, Aurora,v111., a corporation of Illinois No Drawing. Application April 12, 1949,Serial No. 87,110

This invention relates to aluminum base alloys, and it has particularreference to the improvement in castability of aluminum base alloys, asmeasured by reduced surface shrinkage and less porosity in the casting.It also relates to the improvement in other physical properties of analuminum base alloy containing zinc, copper and silicon as majoralloying elements.

Aluminum base alloys of the type prescribed have been used in themanufacture of castings. They have not achieved widecommercialacceptance because they do not have desirable castingcharacteristics and their physical properties are not sufficientlysuperior to other commercial alloys having more desirable castingproperties. One of the principal difficulties suffered by these alloysresides in the inability of securing an acceptable product by sandcasting or by casting in permanent molds. By way of explanation, whenthe cast molten alloy cools down through the liquids range, the changefrom a liquid state to a solid state does not occur immediately.Instead, crystals or nuclei are formed which grow into a matrix havingmicroscopic voids caused by the decrease in volume of the liquid as itassumes crystalline form. The voids that are formed are called poreswhen of small dimension and widely distributed, or pin holes, if thevoids collect in certain areas.

These voids constitute low pressure areas and unless they are quicklyfilled, the casting surfaces may actually collapse to form depressedareas, characteristic of surface shrinkage, accompanied by undesirablecrystal structure. Collapse to form surface shrinkage usually occurs inregions of relatively thick cross section. In the event that the matrixis sufliciently set to resist the effect of shrinkage forces, or in theevent that gases originally dissolved in the metal fill the voids, theporosity defect remains as a permanent part of the casting. When eitherof these conditions prevail, a defective casting is produced which maybe inadequate for the use for which it was intended.

Alloys of the type described are especially diflicult to handle whencasting about a core in permanent molds. Their inferior castingcharacteristics causes undesirable sticking of the core. This oftenleads tothe destruction of the casting and excessive damage to the mold.

5 Claims. (Cl. 75-141) It is an object of this invention to provide analuminum base alloy having improved castability when cast in sand orpermanent molds.

Another object is to formulate for improvements in castability and otherphysical properties in an alloy composed chiefly of aluminum andcontaining silicon, copper and zinc as major alloying elements.

A further object is to provide an aluminum base alloy characterized byimproved physical properties and improved castability when compared toalloys of corresponding composition heretofore produced.

Still another object is to provide a heat treatable aluminum base alloycontaining silicon, zinc and copper as major alloying elements andcharacterized by improved castability and strength when fabricated bysand or permanent mold casting methods.

A still further object is to produce an aluminum base alloy havingphysical properties which may be improved by solution heat-treatment andwhich may be further improved by artificial agemg.

This is a continuation-in-part of my 00- pending application, Serial No.87,109, filed on this same date and entitled Aluminum Base Alloyswherein description is made to the im-- provement in castability andphysical properties in an aluminum base alloy by the addition ofchromium and/or manganese with or without titanium to an aluminum basealloy for casting in green sand or permanent molds. The additions of theminor alloying elements have particular merit when the aluminum basealloy is constituted with copper, silicon and zinc as the major alloyingelements present in amounts ranging from 2 to lpercent copper, 2 to 8percent zinc, 2 to 8 percent silicon and the sum of iron and nickelimpurity is less than 0.75 percent.

I have discovered that physical properties of the desired character andimproved castability may be secured by the addition with the elementsemployed in the parent application of a small amount of zirconium as anadditional alloying element. By the further addition of zirconium,improvements are secured which cannot be achieved by a correspondingcomposition, devoid of zirconium or by increasing the ratio of elemeritschromium, manganese or titanium. Zir.

conium in amounts ranging from 0.05 to 0.30 percent is suflicient andbest results are secured when zirconium in combination with chromium isadded in an amount ranging from 0.10 to 0.25 percent.

Unlike chromium, zirconium offers some grain refining characteristics ineither sand or chill casting whether chromium or titanium are present ornot. Unlike titanium, however, zirconium is not detrimental to castingproperties when chromium or manganese also is present. In chill orpermanent mold casting, zirconium further improves castability with orwithout chromium, manganese and titanium.

These improved characteristics are shown by the following charts madefrom tests of aluminum base alloys containing impurities to the extentof 0.46 percent iron, 0.04 percent nickel and 0.15 percent manganese.Table I gives the physical properties developed by sand casting andTable II gives the physical properties developed by the particular alloyin permanent molds.

TABLE I Physical properties developed m sand castmg 5. 4 5 4 5. 4 5. 43. 3.0 3.0 3.0 5.4 4 5.4 5.4 0. 25 0. 25 0. 25 0 19 0.19 0.19 Titanium0.10

Grain Size, diam. in mm. 1.43 1.66 1.11 1.11 0.3 Shrinkage Very SlightMe- Slight Meheavy dium dium As Cast:

ultimate strength 25,500 26, 500 20,300 26,900 26,200 yield strength i-13, 000 13,000 14,800 15,600 14, 900 Heat Treated:

ultimate strength 32,900 33,700 32,400 31,500 30,800 yield strength 16,900 10,300 16, 300 16,700 17,200 Heat Treated, Aged, ultimate 46, 20046,900 44, 700 47, 900 44,900

TABLE II Physical properties developed by permanent mold casting Zinc5.4 5.4 5.4 5.4 5.4 Copper 3 0 3.0 3.0 3.0 3.0 Silicon 5 4 5.4 5.4 5.45.4 Chromium 0. 25 0. 25 0. 25 Zirconium..- 0.19 0.19 0.19

Titanium.... 0.10

Grain Size, diam. in mm... 0.45 V 0.52 0.40 0. 47 0. 30

cry ihrnkage ..Medium Slight Slight None None s ast:

Ultimate strength 30,000 30, 900 29,800 30,100 31,800 yield strength13,450 12,400 15,300 15,700 16,000 Heat Treated:

ultimate strength 36,500 38,400 40,900 41,200 39,600 yield strength16,400 16,900 17,000 16,300 16,700 Heat Treated, aged, ultimate 50,10049, 200 5'1, 900 52,800 49, 700

It will be apparent that the addition of zirconium alone to the basealloy gives certain reduction in grain size in both sand and permanentmold casting, a reduction which is far greater than that secured by theaddition of chromium alone and less than a combination of chromium andzirconium but not less than that secured by the further addition oftitanium. The addition of zirconium alone also gives improvement incastability, but the improvement is not as marked as that secured by theaddition of zirconium in the present of chromium. Further, the additionof zirconium is more effective in most instances than an addition ofchromium but the combination of zirconium and chromium with or withouttitanium gives best results in almost every case. While the physicaldata presented is for the system zirconium, chromium and titanium, itshould be understood that corresponding results will be secured whenmanganese is used in whole or in part for chromium, though ordinarilyres ent in correspondingly larger proportion by weight.

As used in the tables, the term heat treated refers to solution heattreatment of the casting for 6 hours at 935 to 945 F. followed byquenching in hot water. Heat treatment time may be extended or shorteneddepending upon the weight of the casting, and heat treatment may becarried out at lower temperatures with a corresponding increase in time.The term aged" refers to artificial ageing of the heat treated castingto precipitate out elements or compounds put into solid solution duringheat treatment. Arti ficial ageing in the tested compositions wascarried out by exposure of the heat treated casting to 305 to 315 F. forabout three hours.

A very decided advantage is observed in the use of my new alloy inpermanent mold casting. The alloy sets more rapidly in the mold with theconsequent desirable advantage in that the molding cycle can be greatlyshortened. For example, in one operation, a casting formed with my alloycomposition can be removed after 1 to l /2 minutes in the mold, while acorresponding composition without zirconium and chromium or chromium andtitanium requires a setting time of 1 to 2 minutes. This enables theshortening of the time cycle by about 30 percent. Furthermore, thereduced shrinkage occasioned by the improved casting characteristics ofthe alloy permits casting in permanent molds without the dimcultiesheretofore occasioned upon casting about a core.

It will be apparent from the description that I have produced a new andimproved aluminum base alloy containing zinc, copper and silicon, whichalloy has greatly improved castability as measured by shrinkage andporosity and also has considerably better physical properties. The alloycorresponding to my invention is an alloy having desirable physicalproperties which may be improved by artificial ageing at relatively lowtemperatures.

It will be understood that changes may be made in the ratio of materialsand compositions within the limitations prescribed and their method oftreatment without departing from the spirit of the invention, especiallyas defined in the following claims.

What is claimed is:

1. An aluminum base alloy consisting essentially of 2 to 4 percentcopper, 2 to 8 percent zinc, 2 to 8 percent silicon, 0.05 to 1.00percent chromium, 0.05 to 0.30 percent zirconium, the balance beingaluminum with less than 0.75 percent impurities made up of iron andnickel.

2. An aluminum base alloy consisting essentially of 2 to 4 percentcopper, 2 to 8 percent zinc, 2 to 8 percent silicon, 0.05 to 1.0 percentchromium, 0.05 to 0.3 percent zirconium, 0.05 to 0.20 percent titanium,the balance being aluminum with less than 0.75 percent impurities madeup of iron and nickel.

3. An aluminum base casting alloy consisting of from 2 to 4 percentcopper, 4 to 8 percent zinc, 2 to 8 percent silicon, 0.10'to 0.45percent chromium and 0.10 to 0.25 percent zirconium, the balance beingaluminum with less than 0.75 percent impurities in the form of iron andnickel.

4. An aluminum base casting alloy consisting of from 2 to 4 percentcopper, 4 to 8 percent zinc, 2 to 8 percent silicon, 0.10 to 0.45percent chromium, 0.10 to 0.25 percent zirconium, and 0.05 to 0.15percent titanium, the balance being alumiwith less than 0.75 percentimpurities in UNITED STATES PATENTS the form of iron and nickel. NumberName 7 Date 5. An aluminum base casting alloy consisting 1,572,439Johnston 9, 1926 essentially of from 2 to 4 percent copper, 2 to 82,043,355 Kener June 9, 1936 percent zinc, 2 to 8 percent silicon, anelement 5 2,093,031 Bates 2 1937 selected from the group consisting of0.05 to 1.00 2,280,170 stroup Apt 21 1942 percent chromium, 0.15 to 1.5percent manganese 2,290,016 Bonsack July 14 1942 and mixtures thereof,and 0.05 to 0.30 percent zirconium, the rest being aluminum with lessFOREIGN PATENTS than 0.75 percent impurities made up of iron 10' NumberCountry Date and nickel, 576,230 Great Britain Mar. 25, 1946 A LWILLMORE, 64,251 France Apr. 23, 1941 OTHER REFERENCES REFERENCES CITED15 Manual of Aluminum Castmg Alloys, pub- The following references areof record in the lished by the Aluminum Research Institute, Chifile ofthis patent. cago, 1947, page

1. AN ALUMINUM BASE ALLOY CONSISTING ESSENTIALLY OF 2 TO 4 PERCENTCOPPER, 2 TO 8 PERCENT ZINC, 2 TO 8 PERCENT SILICON, 0.05 TO 1.00PERCENT CHROMIUM, 0.05 TO 0.30 PERCENT ZIRCONIUM, THE BALANCE BEINGALUMINUM WITH LESS THAN 0.75 PERCENT IMPURITIES MADE UP OF IRON ANDNICKEL.